Naming the Mail, Telegraph, Express, and Sun – who broke the story last week – Corbyn said: It’s easy to laugh, but something more serious is happening.

“Publishing these ridiculous smears that have been refuted by Czech officials shows just how worried the media bosses are by the prospect of a Labour government. They are right to be.”

And in an apparent warning to media owners over Labour support for tougher press regulation and part two of the Leveson Inquiry, he added: “Change is coming.”

The 86-second long video has had nearly 1m views, 13,000 retweets and 28,000 likes at the time of writing.

In a leader column today, headlined: “Memo to the BBC: He will come for you too,” the Mail described Corbyn’s video as “sinister” and said it was still waiting for his response to eight questions it claimed he ‘must answer’.

The paper said: “The right to report facts and express views that may be uncomfortable to politicians – right, left or centre – is the very bedrock on which democracy rests.

“And though the Labour leader seeks to laugh off reports of his meetings in the 1980s with Czech agent Jan Sarkocy as ‘ fantasies, smears and lies’, it is an undisputed fact that they took place.”

The Mail quoted a Downing Street spokesperson who told the paper: “Shining a light into dark corners and asking awkward, uncomfortable questions is the Press’s job.

“It is the job of elected politicians to provide answers, not to complain or seek to shoot the messenger because they are being submitted to legitimate questioning.”

The Sun, which originally broke the “Agent Cob” story, has claimed that none of the major broadcasters showed Corbyn’s video in their bulletins because he has refused to give interviews to “explain his spy links”.

ITV’s Robert Peston tweeted: “Very strong attack by Jeremy Corbyn on newspapers and their ‘billionaire owners’ who alleged he had improper relationship in 1980s with Czech spy.

“But if he really wanted to challenge them, why isn’t he doing TV interviews on it, given our impartiality?”

BBC Breakfast presenter Steph McGovern asked Corbyn if he was a “Czezh spy” as he delivered a speech to manufacturers earlier this week, to which he answered: “No.”

Responding to a Daily Mail reporter’s question on whether he would open up his Stasi files on his past, Corbyn said: “I’m very sorry that the Daily Mail has reduced itself to reproducing some nonsense that was written in The Sun beforehand.”